Country diary

Thursday was the day of the emperors. The timing was perfect: a day with flashes of brilliant sunshine book-ended by grey days of rain. It may have begun the previous night or just before dawn, but the nymphs had already settled on their yellow-flag iris leaves by the time the sun struck the pond and the air felt tropically warm.

The dragonfly nymphs abandoned the water to climb into the leaves above, blinded and suddenly vulnerable. They had done this together, six of them, and since the summer day a female emperor dragonfly seeded the pond with her eggs, three or four years ago, this was always going to be their defining moment.

Each nymph is 45mm long, with greeny-brown, pond-coloured camouflage. The formidable jaws have been folded and sealed shut in a head whose great eyes are now blank and opaque. The powerful 20mm legs have clawed into the iris leaves. Inside their hardened exoskeleton, a miraculous alchemy takes place and another creature forms. The nymph's thorax splits open and the emperor dragonfly pushes out, head first, its new body still attached by white breathing tubes at first. The dragonfly struggles clear of its former self, hanging on to the leaf above.

Implausibly, the adult is 70mm long, with a massive head, a thorax like a motorbike petrol tank and a long, thin, yellow and black abdomen. But the most impressive differences are the wings - two pairs of intricately black-veined lace, each 50mm long by 20mm wide. The wings lie down the body, but as the new creature warms, the wings rise. They shimmer and vibrate until the 80-million-year-old process of transformation is complete. By the end of the day they have all flown away, except one that died. I hold it now with incomprehension and awe.